1. Field of the Invention
Embodiments of the present invention generally relate to drilling and completing wellbores. More specifically, embodiments of the present invention relate to drilling and completing wellbores from within a wellhead.
2. Description of the Related Art
In conventional well completion operations, a wellbore is formed to access hydrocarbon-bearing formations by the use of drilling. In drilling operations, a drilling rig is supported by the subterranean formation. A rig floor of the drilling rig is the surface from which casing strings, cutting structures, and other supplies are lowered to form a subterranean wellbore lined with casing. A hole is located in a portion of the rig floor above the desired location of the wellbore.
Drilling is accomplished by utilizing a cutting structure, preferably a drill bit, that is mounted on the end of a drill support member, commonly known as a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on the drilling rig, or by a downhole motor mounted towards the lower end of the drill string.
After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore. Casing isolates the wellbore from the formation, preventing unwanted fluids such as water from flowing from the formation into the wellbore. An annular area is thus formed between the string of casing and the formation. The casing string is at least temporarily hung from the surface of the well. A cementing operation may then be conducted in order to fill the annular area with cement. Using apparatus known in the art, the casing string may be cemented into the wellbore by circulating cement into the annular area defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of interest in the formation behind the casing for the production of hydrocarbons.
As an alternative to the conventional method, drilling with casing is a method often used to place casing strings of decreasing diameter within the wellbore. This method involves attaching a cutting structure in the form of a drill bit to the same string of casing which will line the wellbore. Rather than running a cutting structure on a drill string, the cutting structure or drill shoe is run in at the end of the casing that will remain in the wellbore and be cemented therein. Drilling with casing is often the preferred method of well completion because only one run-in of the working string into the wellbore is necessary to form and line the wellbore per section of casing placed within the wellbore.
After the wellbore has been lined with casing to the desired depth, the casing is perforated at an area of interest within the formation which contains hydrocarbons. The hydrocarbons flow from the area of interest to the surface of the earth formation to result in the production of the hydrocarbons. Typically, hydrocarbons flow to the surface of the formation through production tubing inserted into the cased wellbore.
Drilling and completing each wellbore typically requires a separate drilling rig, a separate wellhead, and separate associated drilling equipment per wellbore. A wellhead is usually located at the surface of each wellbore, below the drilling rig, and may include facilities for installing a casing hanger for use during well completion operations. The casing may be suspended from the casing hanger during various stages of the well completion by use of a gripping arrangement of slips and packing assemblies (e.g., packing rings). The wellhead also usually includes production equipment such as a production tubing hanger for suspending production tubing, means for installing the valve system used during production operations (“Christmas tree”), and/or means for installing surface flow-control equipment for use in hydrocarbon production operations.
A blowout preventer stack (“BOP stack”) is often connected to the top of the wellhead and located below the drilling rig to prevent uncontrolled flow of reservoir fluids into the atmosphere during wellbore operations. The BOP stack includes a valve at the surface of the well that may be closed if control of formation fluids is lost. The design of the BOP stack allows sealing around tubular components in the well, such as drill pipe, casing, or tubing, or sealing around the open hole wellbore. A sealing element is typically elastomeric (e.g., rubber) and may be mechanically squeezed inward to seal drill pipe, casing, tubing, or the open hole. In the alternative, the BOP stack may be equipped with opposed rams.
Historically, one assembly per well drilled and completed, the assembly including a drilling rig, wellhead, and associated drilling and wellhead equipment, has been utilized at multiple surface locations. Therefore, a wellhead and BOP stack must be installed for each well with each drilling rig. Utilizing multiple drilling rigs with their associated wellheads and BOP stacks over the surface of the earth incurs additional cost per drilling rig. The expenditures for each drilling rig, wellhead, and associated equipment; the purchase of and preparation of the additional surface land necessary per drilling rig; and the requirement for additional personnel to install and operate each assembly represent the increased costs. Additionally, safety concerns arise with each drilling rig and wellhead utilized for drilling and completion of a wellbore.
To increase safety and reduce cost per wellbore, it has been suggested that one drilling rig and associated wellhead may be utilized to drill and complete multiple wellbores. When one drilling rig is utilized to complete multiple wellbores, the drilling rig must be moved to each new location to drill and complete each well. Each moving of the drilling rig and wellhead incurs additional cost and provides additional safety risks. At each new location to which the drilling rig is moved, the wellhead must be removed from the old location and then re-installed at the new location by drilling, thus providing additional cost and safety concern per well drilled. Translating the position of the drilling rig and wellhead also requires removing the BOP stack and other drilling equipment from the old location, and then “rigging down” the drilling equipment, including the BOP stack, at the new location. Changing drilling rig position further requires otherwise preparing the wellhead for drilling and completion operations at the location to which the wellhead is moved, such as “tying back” the casing within the wellbore to the surface by connecting a casing string to the casing so that a sealed fluid path exists from the casing to the surface. Furthermore, any change in position of the drilling rig provides the risk of a blowout, spillage, or other safety breach due to disturbance of wellbore conditions.
A recent development in drilling and completing multiple wellbores from one drilling rig and associated wellhead involves directionally drilling the wellbores from one drilling rig and wellhead from proximate surface locations. Directional drilling may be utilized to deviate the direction and orientation of each wellbore so that the multiple wellbores do not intersect. If the wellbores are prevented from intersecting, each wellbore becomes a potentially independent source for hydrocarbon production, often from multiple areas of interest or hydrocarbon production zones.
Because of regulations permitting a limited number of drilling platforms which may be utilized to drill offshore wells, wellbores are often deviated from vertical to increase the amount of wells which may be drilled from a single platform. When drilling an offshore wellbore, a preformed template may be used to guide the location and diameter of the wellbores drilled from the drilling rig. The wellbores are drilled from the template along the well paths dictated by the template to the desired depths.
Directionally drilling the wellbores from one drilling rig and wellhead at proximate surface locations does not alleviate the inherent safety and economic problems which arise with moving the drilling rig and, consequently, the wellhead, as described above. The current apparatus and methods for drilling multiple wellbores from the nearby locations still require at least slight movement of the drilling rig and associated wellhead along the surface. Even slight movement, e.g. 6-8 inches of movement, of the drilling rig along the surface, often termed “skidding the rig”, imposes the additional costs and safety risks involved in removing the wellhead and BOP stack from the first location and “rigging down” the drilling rig, including preparing the wellhead and the BOP stack, for subsequent operations at the second location.
There is therefore a need for a method and apparatus for drilling and completing multiple wellbores from one drilling rig and wellhead without moving the drilling rig or wellhead. There is a further need for an apparatus and method which provides a decrease in the land, cost, and time necessary to drill and complete multiple wellbores. There is a further need for an apparatus and method for completing multiple deviated wellbores from one drilling rig and associated wellhead without moving the drilling rig. There is a yet further need for a more aesthetically and environmentally pleasing method for drilling and completing multiple wellbores.